In situ-generated chiral iron complex as efficient catalyst for enantioselective sulfoxidation using aqueous H₂O₂as oxidant

Abstract

A series of amino alcohol-derived, Schiff-base ligands L1-L4 were synthesised and characterized. Iron complexes of these ligands [FeL1(acac)], [FeL2(acac)], [FeL3(acac)] and [FeL4(acac)] were generated in situ to catalyze the asymmetric oxidation of prochiral sulfides using aqueous H 2 O 2 as a terminal oxidant. One of these complexes [FeL1(acac)] was identified as a very efficient catalyst for the enantioselective oxidation of a series of alkyl aryl sulfides with excellent enantioselectivity (75-96% ee), conversion (up to 92%) and chemo selectivity (up to 98%). During the optimization process, a series of electron-donating benzoic acid derivatives were found to favour both conversion and enantioselectivity.

Modern Stereoselective Synthesis of Chiral Sulfinyl Compounds

“…67−69 Chiral salen-type Fe(III) complexes were also used in successful sulfoxidations with peroxides. 70,71 Nishiguchi et al applied iron(III) complex with a Schiff base 11 in preparation of proton pump inhibitors and received esomeprazole 2 in 87% yield (12% of sulfone was formed) and >99% ee (Scheme 6). 72 Optimized reaction conditions included slow addition of aqueous hydrogen peroxide and the use of lithium 4dimethylaminobenzoate additive 12 and ethyl acetate as a A new concept of asymmetric counteranion-directed catalysis (ACDC) 73 was tested by Liao and List; the catalyst 13 consisted of an achiral iron(III) cationic complex and an enantiopure phosphate counteranion.…”

“…Modified Schiff bases were introduced by several research groups as chiral tridendate ligands for vanadium­(IV), typically applied as VO­(acac) 2 in a two-phase system with hydrogen peroxide as oxidant. − Manganese was used in combination of salen , or another tetradendate, N4 ligand 8 ; the latter, with carboxylic acid 9 as additive and H 2 O 2 as oxidant, allowed highly enantioselective, gram-scale preparation of various sulfoxides also in the flow system (Scheme ). − Chiral salen-type Fe­(III) complexes were also used in successful sulfoxidations with peroxides. , Nishiguchi et al applied iron­(III) complex with a Schiff base 11 in preparation of proton pump inhibitors and received esomeprazole 2 in 87% yield (12% of sulfone was formed) and >99% ee (Scheme ). Optimized reaction conditions included slow addition of aqueous hydrogen peroxide and the use of lithium 4-dimethylaminobenzoate additive 12 and ethyl acetate as a solvent.…”

Schiff base complex conjugates of bovine serum albumin as artificial metalloenzymes for eco-friendly enantioselective sulfoxidation

“…Asymmetric selective oxidation of suldes to sulfoxides is an important reaction that deserves much attention because enantiomerically pure sulfoxides are valuable compounds that have utility as powerful chiral auxiliaries, [1][2][3] ligands, 4,5 organocatalysts 6,7 in asymmetric organic synthesis, [8][9][10] and as active pharmaceutical ingredients. [11][12][13][14][15] Traditionally, catalysis has been divided into three subdisciplines: heterogeneous, homogeneous, and enzymatic catalysis. Although promising metal catalysts 16 have been developed and show encouraging practical potential, issues such as compound stability, efficacy, regio-and stereoselectivity, and environmental toxicity remain to be addressed.…”

Manganese- and Lanthanide-Based 1D Chiral Coordination Polymers as an Enantioselective Catalyst for Sulfoxidation

“…Chiral sulfoxides are valuable subunits for the pharmaceutical industry and biological systems , Thus, considerable progress has been made developing catalysts for asymmetric sulfoxidation over the past few decades. , Sulfoxides were synthesized starting from achiral molecules in the presence of enantiomeric pure catalyst. ,,− Mainly homogeneous catalysts derived from transitional metals, such as titanium, , vanadium, chromium, manganese, − and iron, , ligated by chiral moieties and a few metal-free systems were used in the past. Exceptional efficiency in the enantioselective oxidation of sulfides and olefins has been observed by using these homogeneous systems.…”

“…Therefore, the development of new asymmetric heterogeneous catalysts remains a continuing challenge. ,,, In this regard, the synthesis of chiral metal organic frameworks (CMOFs) , and chiral coordination polymers (CCPs) has been an attractive research area . One method for the generation of CMOFs is the use of chiral metalloligands as linkers between the knots.…”